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UCC28070: UCC28070 PFC controller over current error

Part Number: UCC28070

Hello,

i'm try to design AC/DC controller with pfc controller. I use ucc28070pw controller.  I make a prototype and meet a problem. 

1 )  when disconnect to load pfc run correctly input: 115 VAC output: 400 VDC but when connect pfc to load and draw curent output voltage dicrease to 160 VDC. 

controller doesn't increase duty cycle range in my opinion controller behave like over current protectiopn.

Actually i use TI application note for referance design.

attached file you can see design files. UCC28070_Sematic.pdfUCC28070_Sematic2.pdfCan you please have look design shematic and guide me about current sensing.

  • Hello Dogan

    Can you post your schematic and PCB layout here (Gerber files are ok) and I can review them and see if I can spot anything. Otherwise, can you post a screen shot of the CS signals - CSA and CSB.

    Finally, can you double, double check that your CSA signal is coming from the MOSFET controlled by OUTA and the CSB signal is coming from the MOSFET controlled by OUTB. I know it sounds obvious but this has happened in the past.

    Regards

    Colin

  • Hello Coil,

    Yes. CSA and CSB signals coming to controller but it carried some high frequency noise. Is it posible cousing by noise?  PKLMT, VREF, VSense and VINAC signals are also coming to controller with recommands value. 

    attached files you can see Altium Designer's  Shematics and pcb files. Also Gerber Files.Project Outputs for ACDC_Lancer_Beta_PCB_2.rar

  • Hello Dogan

    I had a look at your layout - I'll try to spend some more time looking at it tomorrow but for now the main thing I spot is that the ground trace from Pin 16 of the UCC28070 is quite long. Ideallly it would connect to the ground plane through a via a the pin.

    One thing you should try is to turn off the B channel by removing the gate drive resistor and tying the MOSFET gate to its source. This will halve the power that the board can handle of course but it will remove any interference that may be coming through from one channel into the other.

    Regards

    Colin

  • I consider about zener diode which is used the output of current sense transformer. 33 volt zener is just for protection of reverse voltage? is it must be exactly 33 volt?

  • Hello Dogan

    The diodes are used to limit the reset voltage seen at the CT secondary the 33V value is not critical. I tried to find a good reference on CT reset but failed so here is a quick summary.

    During the on time there will be a certain voltage*second product built up on the secondary as the secondary current flows in the rectifier diode and resistor - perhaps it would be about 1.7V*9.5us if you had a stage running at 95% duty cycle at 100kHz. This V*s product will cause a flux change in the transformer core which must be reset to its starting value before the start of the next cycle. If the core flux has been changed by an amount proportional to 1.7V*9.5us then we have to apply the same volt second product to reset the flux. Given a 10us cycle time, we have 0.5us to reset the core which will require a voltage of about 32V to be applied.

    A simple resistor can be used, the voltage developed being Imag*Rreset. Hi values of Rreset give high voltages. Or you can clamp the voltage using a zener and accept that the reset may take more time. In the previous example a 33 V zener will give you reset in 0.5us, a 16V zener will reset the core in 1us but this won't allow you to operate at 95%. Essentially, there is a trade off between reset voltage and reset time.

    Hope this helps.

    Regards

    Colin